Edwin Diaz has the highest strikeout rate in the history of baseball.
Sure, it’s only 26 innings, and even for reliever seasons any “highest strikeout rate” list should probably start at 50 innings, but what the 22-year-old Mariners rookie has done so far deserves some attention. Diaz has 52 strikeouts in 26 innings, which is 18.0 per nine innings. Aroldis Chapman currently holds the strikeout rate record with 17.7 per nine innings in 2014—when he whiffed 106 in 54 frames—and there are only 10 total seasons in which a pitcher with 25-plus innings topped 15.0 SO/9.
Diaz was Seattle’s third-round draft pick in 2012 and had some pretty good success as a starter in the minors. Last season at Double-A he started 20 games and posted a 103/37 K/BB ratio in 104 innings, which is really good for a 21-year-old. Diaz began this year back at Double-A, still starting, and fared even better with a 3.10 ERA and 38/5 K/BB ratio in 29 innings through mid-May. And then the Mariners shifted him to the bullpen. Four weeks and 10 relief appearances later, he was in the majors.
Diaz was called up by the Mariners on June 6. It took two batters for his first career strikeout, which came via Tyler Naquin swinging through a 100 mph fastball:
When asked why the team shifted Diaz to the bullpen despite his strong work as a starter in the minors, general manager Jerry Dipoto said: “The changeup has never really been easy for him. … So, the likelihood of him picking up that third pitch was maybe a little bit more remote.” Diaz had the ability to be a good starter, particularly if his changeup ever improved, but Dipoto and company felt he had the ability to be an amazing fastball-slider reliever now.
Through two months as a big leaguer Diaz has thrown 440 pitches and exactly one of them has been classified as a changeup. June 19 against the Red Sox. Diaz started David Ortiz with the lone “changeup” clocking in at 89 miles per hour. It was a ball and one pitch later the Mariners decided to just intentionally walk Ortiz. And that’s the full extent of Edwin Diaz’s changeup usage. He’s thrown 314 pitches since then, all of them fastballs and sliders, and nearly all of them nasty as hell.
Diaz’s fastball, thrown about three-fourths of the time, averages 97 mph and has generated 15 percent swinging strikes. His slider, thrown about one-fourth of the time, averages 87 mph and has generated 38 percent swinging strikes. Blend those two deadly pitches together and Diaz is tied for the MLB lead with a swinging strike rate of 20 percent. Whenever opponents have made contact off Diaz they’ve actually had incredible success—.458 BABIP, 18.8% HR/FB—but those instances are rare.
Last month he got 11 consecutive outs via strikeouts to set a Mariners record. He’s struck out 52 of the 113 batters he’s faced overall this season, which leads baseball at 46 percent. Dellin Betances and Andrew Miller are tied for second at 44 percent and no one else is above 38 percent. Chapman in 2014, Craig Kimbrel in 2012, and Carter Capps (and his quasi-legal delivery) in 2015 are the only pitchers ever with 25-plus innings and a strikeout rate above 46 percent.
Diaz has a 52/8 K/BB ratio in 26 innings for Seattle and his 1.73 ERA is matched by an equally miniscule 1.76 FIP and 1.66 DRA. Since moving to the bullpen full time at Double-A in mid-May he’s thrown 38 innings with a 68/10 K/BB ratio and 1.19 ERA while holding opponents to a .197 batting average between the minors and majors. He’s currently riding a 10-appearance scoreless streak in which Diaz has struck out 20 of 37 batters and issued two walks.
Tuesday night Diaz picked up his first career save by striking out the side versus the Red Sox to preserve a 5-4 victory. It was the fifth time Diaz has struck out the side in his 13 one-inning appearances. He got Jackie Bradley swinging on a 98 mph fastball, Sandy Leon swinging on an 86 mph slider, and Andrew Benintendi looking on a 99 mph fastball. It was the full Edwin Diaz Experience, complete with Mariners play-by-play announcer Dave Sims going nuts while calling him “The Electric One.”
Diaz seems aware of just how dominant he’s been and can be now that the Mariners have quickly turned to him in the closer role. “I’m ready to be the closer,” the rookie with all of 43 professional relief appearances told reporters before Tuesday’s game when asked about replacing experienced but struggling closer Steve Cishek. “I like to pitch in pressure [situations]. I feel more confident when I’m in a close game. I don’t know why, but I feel very good.”
Diaz may not know why, but Mariners catcher Mike Zunino summed it up after the first of many saves: “He trusts his stuff, but I think anyone would.”
Thank you for reading
This is a free article. If you enjoyed it, consider subscribing to Baseball Prospectus. Subscriptions support ongoing public baseball research and analysis in an increasingly proprietary environment.
Subscribe now